The present invention generally relates to methods of making nanocrystalline rare earth phosphates, utilizable for enhanced lighting and other applications. In particular, the present invention generally relates to methods of making nanocrystalline activated rare earth phosphates useful as one or more of quantum-splitting phosphor, visible-light emitting phosphor, vacuum-UV absorbing phosphor, and UV-emitting phosphor.
Light generation in gas discharge lamps (such as the mercury low-pressure discharge used in common fluorescent lamps) is generally based on photon emission from excited atoms in a gas plasma, which emission can be in the ultraviolet and/or visible regions of the electromagnetic spectrum. Ultraviolet (UV) radiation, the predominant form of such emission, can be converted to useful visible light by a phosphor composition in optical communication with the UV photon, e.g., a phosphor composition on the inside of a lamp's envelope. For the case of a low-pressure mercury discharge, the UV emission concentrates at wavelengths of about 254 nm and about 185 nm.
One drawback of many known mercury low-pressure gas discharge lamps is that most of the phosphors used in current fluorescent lamps are only sensitive to radiation with wavelength around 254 nm. Consequently the mercury discharge radiation at about 185 nm wavelength does not significantly contribute to the overall light output of the lamp. For improved efficiency of known mercury low-pressure fluorescent lamps, intense study has accrued to phosphors capable of utilizing the 185 nm radiation, either by conversion to a higher UV wavelength which other more common phosphors may absorb, or by conversion to a higher visible wavelength, or by quantum splitting, which is the conversion of a single UV photon into two photons of higher (often visible) wavelength. Quantum splitting materials are very desirable for use as phosphors for lighting applications, such as fluorescent lamps. A suitable quantum splitting phosphor can, in principle, produce a significantly brighter fluorescent light source due to higher overall luminous output because it can convert to visible light the part of UV radiation that is not absorbed efficiently by traditional phosphors currently used in commercial fluorescent lamps. Quantum splitting phosphors, therefore, are suitably used in combination with ordinary phosphors that effectively convert the 254 nm UV radiation to visible light.
Although heretofore known quantum-splitting phosphors may theoretically increase the efficiency of fluorescent lights, the inventors of the present invention have found that many heretofore known quantum-splitting phosphors generally have particle sizes too large for fully efficient use, since large particles may scatter the UV light (e.g., 254 nm) which ordinary phosphors are designed to convert, and thus large-particle quantum splitting phosphors may actually impair the efficiency of fluorescent lamps in which they are used.
Thus there is a continued need for cost-effective, simple methods to produce quantum-splitting phosphors that do not suffer from the above inconveniences.